Communications system

ABSTRACT

A communications system connected via a bus capable of transmitting multiplexed packets of control signals and AV signals while providing an environment, which is the same as an environment where connections are made using analog signal lines. A register with a fixed address is taken to be a virtual plug for each of a plurality of equipment. When the plug enable for the input plug is set to 1, an isochronous communication packet for the AV signal on the channel set by the channel number is received. When the plug enable for the output plug is set to one and the isochronous communication packet for the information signal is sent on the channel, then the channel number is set in the channel number field at a transmission speed designated by the DR (Data Rate) field at the bandwidth presented in the bandwidth field.

This is a Continuation of prior applicaton Ser. No. 08/738,465, filedOct. 24, 1996, now U.S. Pat. No. 6,584,099, which is a continuation ofapplication Ser. No. 08/354,119 filed Dec. 6, 1994.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to way of structuring input/output plugsand a digital interface for equipment in a communications system where anumber of items of equipment capable of mixing and transferring aspackets control signals and information signals are connected via a bus.

2. Description of the Related Art

In conventional communication systems where AV equipment such as, forexample, Video Tape Recorders (hereinafter referred to as VTRs),Televisions (hereinafter referred to as TVs) etc. are connected togethervia analog AV signal lines and digital control signal lines, a DDB(Domestic Digital Bus) has been used. Examples of this kind of systemare described in the European patents belonging to the same applicantrelating to this kind of communications system. These patents arepublication number EP 0 604 166, EP 0 610 630, EP 0 604 167 and EP 0 608624. Applications are currently under way for American patents whichwill correspond to these patents.

First, a description will be given of an example of this kind ofcommunications system with reference to FIG. 17. This kind ofcommunications system is equipped with a TV, a VTR 1, a VTR 2, a MultiDisc Player (herinafter referred to as an MDP), and an editor. The VTR 2is also connected to a device which is not compatible with a digitalcontrol signal line (hereinafter referred to as a non-bus compatibledevice).

The AV signal input/output plug for the non-bus compatible device isconnected to input/output plugs of other devices only by plugs describedby P1, P2 and P3, protruding directly out from units known asswitchboxes (SW box) via analog AV signal lines. Commands such asconnection control commands etc. are sent and received by other devicesvia analog AV signal lines and digital control signal lines which areconnected separately. Each item of equipment is also equipped with oneor more functional units, which in the case of a VTR would be a deck forrecording and playing back and a tuner for selecting the signal to bereceived, and in the case of a TV, would be a monitor and an amplifier.There is also an AVC (AV controller) for controlling the operation ofall of the items of equipment, although this is not shown in thediagrams. In the following, these functional units may also be referredto as sub-devices.

Control connection can be carried out in two ways in a communicationssystem structured in this way. These ways, which will be referred to asconnection control method 1 and connection control method 2, will bedescribed in numerical order.

In connection control method 1, information pertaining to the connectionstructure for each device, i.e. which plug is connected to which plug ofan opposing item of equipment and whether plugs are used for input oroutput, is pre-stored by the user. In this way, an output plug which itis considered will make a connection from the sub-device which is to bethe AV signal source to the destination may be selected as requiredwhile the item of equipment is receiving the connection control command.Alternatively, a path may be set up within the device between the inputplug of the designated number and the appropriate output plug, with acommand then being transmitted to the device connected previously to theoutput plug. The object is then achieved at the point in time when thecommand reaches the sub-device within the specific device indicated bythe destination. At this time, commands cannot be transmitted via thecontrol signal line when the device is a non-bus compatible device. Theplug numbers for devices connected to this kind of device therefore haveto be directly specified (for example, in the case in FIG. 17, the inputplug P1 for the VTR 2 is directly specified).

The following is a description with reference to FIG. 18 of the sequencein connection control method 1 when an MDP output is recorded on a VTR 2as a result of instructions from an editor. FIG. 18( a) shows thecommunications sequence and FIG. 18( b) shows the commands.

First, the MDP receives a command giving an instruction to connect thedeck output to the deck of the VTR 2 from the command master (editor)(communication 1). At this time, none of the output plugs of the MDP areconnected to the VTR 2. However, the output plug P3 is connected to theinput plug P1 of the VTR 2, so a command is therefore sent to the VTR 1via a path from the input plug P1 to the switchbox (communication 2).

When the VTR 1 receives this command, none of the output plugs areconnected to the VTR 2 but the output plug P3 is connected to the inputplug P1 of the TV. A command is therefore sent via a path from the inputplug P1 via the switchbox to the TV (communication 3).

When the TV receives this command, it is understood that the output plugP3 is connected to the input plug P2 of the VTR 2 and a command is sentto the VTR 2 form the input plug P2 via the deck (communication 4).

The VTR 2 then receives this command and changes over the switchboxconnection so as to input from the input plug P2 to the deck. Once theVTR 2 completes the process 4, the TV is notified of this completion.Upon receival of this, the TV gives notification to the VTR 1 that theprocess 3 is completed. When the VTR 1 then receives this, it givesnotice to the MDP that the process 2 has been completed. Upon receivingthis, the MDP gives notice to the command master that the process iscompleted. These packets are omitted from the diagrams.

Here, an editor has been set up as the command master. However, ratherthan setting an editor up on the communications system, a structure maybe adopted where the MDP and the VTR have command master functions.

In a second connection control method, a single central item ofequipment (in the following, this is an AV center) manages all of theconnection information regarding which kinds of equipment are connectedtogether via which numbered ports in which directions. If a commandrequesting AV signal connection via the digital control signal line isthen received, this command is sent via the digital control signal lineto the target device. The target device then receives this command andchanges over the input/output. At this time, it is possible to designatethe sub-device by category via the initial connection request from thecommand master (by BS, CS etc. which are more in line with theobjectives, rather than by a tuner etc.). However, at the time of aconnection request, an item is only aware of its own plug structure.

The following is a description with reference to FIG. 19 of the sequencein a connection control method 2 when a TV is taken as an AV center andoutput from an MDP is recorded by a VTR 2. Here, FIG. 19( a) shows thecommunications sequence and FIG. 19( b) shows the commands.

First, the TV receives a command from the command master instructing itto connect the MDP deck output to the deck of the VTR 2 (communication1). The TV then receives this command and sends a command to the MDP tothe effect that the output for the deck sub-device is to be outputtedfrom the output plug P3 (communication 2).

If the MDP receives this command, the switchbox is changed over so thatthe deck output is connected to the output plug P3 and notification ofthe completion of the changeover process is then sent to the TV. If theTV then receives this information, a command is sent from the input plugP1 via the output plug P3 to the VTR 1 (communication 3).

If the VTR 1 receives this command, the switchbox is changed over sothat a connection is made from the input plug P1 to the output plug P3and notification of completion of the changeover process is sent to theTV. If the TV then receives this notification, a command is sent fromthe input plug P2 to the deck to be inputted to the VTR 2 (communication4).

Providing the VTR 2 receives this command, the switchbox is changed overso as to input from the input plug P2 to the deck. The TV is thennotified when the changeover process is complete.

If the TV then receives notification of completion from the VTR 2,notification of completion of the connection is sent to the commandmaster.

However, with connection control method 1, the digital control signalline becomes confused as a result of commands being transmitted betweenitems of equipment which neighbor each other. It is also possible thatan infinite loop may be formed depending on the settings of items ofequipment in the connection line. It is also necessary to know thestructure of the items of equipment which it is intended to control withthe command master and the structure of the connections between theequipment in the overall system, so the plug numbers can be designateddirectly.

Also, in connection control method 2, no matter how simply a connectionis made between a plug for an item of equipment and the preceding itemof equipment to which the plug is connected, this cannot be achievedwithout a request being made to the AV center. Further, designation canbe made using the sub-device category at the time of a connectionrequest, but plug set-up can only be achieved for an item of equipment'sown plugs, for which the structure is known.

It is therefore apparent that connection control of a variety of AVsignals by holding connection information for input/output plugs on theoutside of items of equipment and present within interfaces is notappropriate. It is therefore the object of the present invention toprovide a communications system capable of resolving these kinds ofproblems.

SUMMARY OF THE INVENTION

In order to resolve the aforementioned problems, in the presentinvention, a communications system has a number of items of equipmenthaving input/output plugs and containing functional units connected viaa bus capable of transferring packets containing combinations of controlsignals and information signals. The input/output plugs for the items ofequipment within the system are then given attributes and handled in thesame way as the functional units within the items of equipment.

Here, the input/output plugs may also be only for inputting andoutputting information signals and may not be connected to the bus.Alternatively, the input/output plugs may be bus channels. Items ofequipment within the system may be VTRs, TVs and MDPs etc. In this case,the information signals may be image signals and/or audio signals.

Also, in the present invention, a communications system has a number ofitems of equipment, connected via a bus, capable of transferring packetscontaining combinations of control signals and information signals,where virtual plugs for inputting and outputting information signals areset up at each item of equipment within the system and informationsignal connections between each of the items of equipment are made bycontrolling connections between the plugs. It is preferable to carry outthe inputting of the information signals and the outputting of theinformation signals independently by setting up the virtual plugsseparately for input and output.

Further, in this invention, connections made between the items ofequipment using virtual plugs and connections made between functionalunits for inputting and outputting information signals within the itemsof equipment and virtual plugs for the items of equipment are carriedout independently from each other.

Also, the virtual plug may consist of at least plug enable informationand an information signal channel number written in a fixedly allottedmanner to a region of a storage means such as, for example, a registeretc. and inputting and outputting of information signals usingwritten-in channels can be carried out by controlling the plug enableinformation. In the case of an output plug, the information signaltransfer speed and bandwidth are written in and the outputting of theinformation signal is carried out for the written in channel at thewritten in transfer speed and bandwidth. Also, an item for preventingthe written-in information from being overwritten is set up as it ispreferable to provide protection for the connection conditions.

According to the present invention described in detail above, input andoutput plugs for communications equipment are assigned numbers and arehandled and categorized in the same way as for sub-devices. In this way,input and output plugs can be designated in the same way as forsub-devices while connection control commands are being configured. As aresult of this, it is not necessary for the command master to be awareof the connection structure of the opposing item of equipment or theconnection configuration for the items of equipment in the overallsystem. Items of equipment can therefore be subjected to control simplyby making a designation using a category. The connection controltherefore becomes simple and clear, so that rapid connection control canbe achieved while requiring only a small number of communications.

According to the present invention, a control system for makingconnections between digital plugs is set up. This system is set upindependently from a system for making connections between sub-deviceswithin the items of equipment and digital plugs. In this way, thedifference between the channel which depends on the digital bus and thebandwidth is assimilated and an environment is provided which is thesame as being physically connected via an analog signal line. It istherefore possible to interface via a digital plug without having tograft a the concept of a digital bus. characteristic to internalconnection control systems for existing equipment. This means thatexchangeability with existing command sets can be maintained. By thensetting up the digital plugs within a digital I/F communications IC,digital I/F compatibility can be maintained even without acommunications control microcomputer. It is therefore possible to makeequipment at a low price.

Also, it is no longer necessary to make requests to the AV center whichcarries out centralized processing of connection information whentransferring commands from one place to the next in the way that wasnecessary in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an example of a structure of a communicationssystem to which this invention is applied;

FIG. 2 is a view showing an example of the communications cycleoccurring in the communications system in FIG. 1;

FIG. 3 is an example view showing the internal structure of the VTR inFIG. 1 in more detail;

FIG. 4 is a view showing an example of the internal structure of thenon-bus compatible device in FIG. 1;

FIG. 5 is a view showing the sub-device categorization;

FIG. 6 is a view showing an example of a category which is actuallycompatible with a sub-device number;

FIG. 7 is a view showing sub-device categorization;

FIG. 8 is a view showing an example of a category/address which isactually compatible with a plug number;

FIG. 9 is a view showing an example of a category/address compatiblewith an actual plug number for which the name has been changed to thatof the specific opposing item of equipment to which it is connected;

FIG. 10 is a view showing the connection control when the output from anMDP using a categorized plug is recorded on a VTR 2;

FIG. 11 is a view showing the connection control when the output from acamera present in a non-bus compatible device connected to the inputplug P1 of the VTR 2 which uses a categorized plug is displayed on a TV;

FIG. 12 is a view of an example of a digital plug;

FIG. 13 is a view showing the connection control when the output from anMDP using a digital plug is recorded on the VTR 2;

FIG. 14 is a view showing an example of a structure for a VTR equippedwith digital plugs;

FIG. 15 is a view showing a further example structure of a VTR equippedwith digital plugs;

FIG. 16 is a view showing an example hard disc structure for a hard discapparatus equipped with digital plugs;

FIG. 17 is a view showing the structure of a communications system whereAV equipment is connected by analog signal lines and digital controlsignal lines;

FIG. 18 is a view showing an example of the connection control methodoccurring in the communications system in FIG. 17; and

FIG. 19 is a view showing a further example of the connection controlmethod occurring in the communications system in FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment

The following is a detailed description with reference to the diagramsof

1. a communications system to which this invention is applicable;

2. a sub-device categorizer;

3. a plug categorizer;

4. a specific example of connection control using a categorized plug;

5. a virtual plug set up,

6. a specific example of connection control using a virtual plug; and

7. an example of equipment equipped with a virtual plug, with respect tothe embodiments of this invention.

1. The communication system to which this invention is applicable.

FIG. 1 is a view of an example of a system structure of a communicationssystem to which this invention is applicable. This communication systemis equipped with an MDP, TV, VTR 1, VTR 2 and editor. Connections aremade between MDP and VTR 1, VTR 1 and the TV, the TV and VTR 2 and theeditor and the MDP using P1394 serial buses. An non-bus compatibledevice is also connected at the input plug P1 after the VTR 2.

The input plugs and the output plugs for each of the items of equipmentare independently numbered, with a category being assigned internallyfor each item of equipment. Each plug is arranged so as to be an equaldistance from the sub-device with respect to the center of theswitchbox. It is usual for these input/output plugs to be connected tonon-bus compatible devices. Intermittent attributes (analog line input,digital line input) for the plug categories are held as defaults andspecific opposing connections are held as user entries (These will bedescribed in detail later). There are also cases where AV signal linesfor the audio signals and video signals within the equipment areindependent of each other, but in order to keep the description simple,no discrimination will be made in this case. There is also an AVCsub-device present for controlling the operation of all the items ofequipment, but this is not shown in the diagrams.

Each item of equipment (non-bus compatible items of equipment excluded)is equipped with a digital interface (hereinafter referred to as digitalI/F) for the P1394 serial buses. This digital I/F is a dedicatedcommunications IC for carrying out the transfer of control signal andinformation signal packets.

At the P1394 serial bus, communication is carried out in prescribedcommunication cycles (for example, 125 micro seconds), as shown in FIG.2. The communication of information signals such as compressed digitalvideo signals is carried out both synchronously, where communication iscarried out serially at a fixed data rate, and asynchronously, wherenon-periodical transfers take place in response to the necessary controlsignals such as control commands etc.

There is a cycle start packet CSP at the start of the communicationcycle, after which the period for transferring the packet is set up toensure synchronous communication. It is possible to carry out a numberof synchronous communications by assigning channel numbers 1, 2, 3, . .. N to the packets for carrying out synchronous communications.

After the transfer of the synchronous communication packets for all ofthe channels is completed, the period until the next cycle start packetCSP is used for non-synchronous communications. The non-synchronouscommunications packet (packets A and B in FIG. 2) has the physicaladdresses and logical addresses for the transmission equipment andreceiving equipment. Each item of equipment then takes in the packetwhich has its own address attached.

The control signals and information signals can therefore be mixedtogether and transferred at the P1394 serial bus. As a result, it is nolonger necessary to be aware of the connection structure while thedigital I/F input/output plug for this bus is being handled.

FIG. 3 shows an example of the details of the internal structure of theVTR 1. The P1394 serial bus line (hereinafter referred to as the digitalbus) in this diagram represents a bidirectional line consisting of twolines. This may also consist of one line going in just one direction oritems consisting of three lines or more, depending on the item ofequipment. Analog A/D converters and/or D/A converters are set upbetween the analog line input plugs and the analog line output plugs,and the switchboxes. An OSD generator (on screen display) is alsoconnected to the monitor output plug.

Each sub-device and each plug is connected to either or both the AVsignal input and output for the switchbox. Changeovers then can be madeusing each of the switches SW1 to SW3 within the switchbox. For example,SW1 changes over between the digital input plug, analog input plug. andtuner sub-device. The switch SW3 then changes over between these resultsand the input from the digital I/F. The switch SW2 is then changed overto output either these results, or the play-back input from the decksub-device, from the switchbox. The switch SW2 also changes over whetherto output to the deck sub-device at the time of picture recording. Asthis alternates with the input from the deck, this can be expressedvirtually as two types of inter-locking switches having three positionsover all. It is also possible to change over whether or not to sendoutput to the digital I/F at the switch SW3. As this is alternated withthe input from the digital I/F, this can also be expressed by two kindsof inter locking switches having a total of three positions.

In this way, in this invention, the plug and the functional unit may beconsidered equal while describing the internal structure of the items ofequipment, so that inputs and outputs going to the switchbox may bedistinctly divided. This method of expression may also be applied tonon-bus compatible items of equipment of the kind shown in FIG. 4.

2. A sub-device categorizer.

FIG. 5 is a view of a sub-device categorizer. The sub-device number andcategory type are expressed respectively using ten bit data (B9 to B0).In this way, the decks sub-device number and category type for the VTRmay be shown.

FIG. 6 shows an example of an actual sub-device number and correspondingcategory. This diagram shows a double-deck VTR consisting of a VHS/S-VHSVTR deck 1 and a 8 mm/High deck VTR deck 2.

3. A plug categorizer.

FIG. 7 is a view showing a plug categorizer. In this invention, theinput/output plug and digital bus channel number for each item ofequipment are handled together as a plug and then categorized. The plugnumber and the category type are expressed respectively as ten bit data(B9 to B0).

Numbers from 1 to 64 may be allotted as the plug numbers forinput/output. Also, the input/output plug occurring at the digital bus,i.e. the channel, is selected as one of the channels 1–64 forinput/output, while at the same time making a connection with only oneroute.

The category type shows the category of the item of equipment connectedto plug number 1 to 64. Connection control is then carried out usingthis category, rather than the plug number (refer to the example in FIG.11). With regards to the digital channel, as a specific logical addressfor the opposing item is stored (TV, VTR etc.), this category type isnot used. However, “Digital bus CH?” uses the category designationcommand, “output at arbitrary channel” (refer to the practical examplein FIG. 10).

FIG. 8 is a view showing an example of an actual plug number and acorresponding category/address. This diagram shows an item of equipmentwhere plug 1 uses an analog line input and a monitor output, plug 2 usesan analog line input and an analog line output, and plug 3 uses adigital line output.

As can be seen from FIG. 8, when the category is based on the default,this category is expressed by usual plug attributes such as analoginput/output and digital line input. However, if the category is basedon user settings etc., the categories can be replaced with those forother specific connected items of equipment.

This is shown by the example in FIG. 9. This diagram shows an item ofequipment where plug 1 is used for a camera input and a monitor output,plug 2 is used for a CD input and a video printer output and plug 3 isused for an audio deck output. A digital bus may also be connecteddepending on the system specification, and depending on the plug, thiscan also be considered to be the same as being connected to the opposingitem of equipment. In this case, the address of the opposing item ofequipment on the digital bus is stored.

As described above, with regards to the digital bus, the logical addressfor a specific opposing item of equipment is stored. However, at thesame time, as only one channel is used, even if there is data within theexpression this will only occupy one place. When an item outputs fromitself, a number of items of equipment which input to this channelexist. This means that a number of logical addresses can be stored atone place within the expression. In FIG. 9, an output for a digital buschannel 2 shows that the TV and the VTR 2 are being taken as input.

As the plug and the functional unit can be considered to be the same inthis invention, the plug can be indirectly indicated using the cateowhile connection control is being carried out by another item ofequipment, and the item of equipment which receives the commands canmake a specific determination with regards to the plug.

4. A specific example of connection control using a categorized plug.

1. The case where recording is carried out with the MDP output going tothe VTR 2. The following is a description with reference to FIG. 10, ofthe connection control for the case where the MDP output is recorded atthe VTR 2. Here, FIG. 10( a) shows the communication sequence and FIG.10( b) shows the commands.

First, the MDP receives a command for outputting the deck output fromthe command master (editor) to the digital bus (communication 1). If theMDP can output the output from the deck to the digital bus, this channelnumber (here this is channel 1) is transferred to the command master asan “On command”.

Next, the command master receives the channel number sent from the MDP,and sends an inputted command going from the channel 1 to the deck tothe VTR 2 (communication 3). If input is carried out from the channel 1to the deck, the VTR 2 transmits notification of completion to thecommand master.

In this embodiment, connection control can then be carried out rapidlyby designating the plug using the category “Digital bus channel?”.

2. When the output for a camera present in the non-bus compatible itemof equipment connected to the input plug P1 at the VTR 2 is displayed ona TV.

The following is a description of the connection control when the outputfor a camera present in the non-bus compatible item of equipmentconnected to the input plug P1 of the VTR 2 is displayed on a TV. Here,FIG. 11( a) shows the communication sequence and FIG. 11(B) shows thecommands.

First, a command is received by the VTR 2 to the effect that cameraoutput from the command master has been outputted to the digital bus(communication 1). It is then determined whether the input plug to whichthe camera is connected is P1. If it has been possible to output this tothe digital bus, the outputted channel number is transferred to thecommand master (communication 2).

The command master receives the channel number (here this is channel 1)sent from the VTR 2 and sends a command for inputting from channel 1 tothe monitor to the TV (communication 3). If the TV then inputs from thechannel 1 to the monitor, notification of completion is sent to themaster.

In this way, in the present invention, regarding the analog plug numberwhich was directly designated in the conventional connection controlmethod 1, this is designated as the indirect category known as,“camera”. Also, in the conventional connection control method 2, aconnection request could not be made if the leading plug number for theopposing item of equipment was not known. However, in this invention,the connection request can be made using the category designation in theway described above.

5. Virtual plug set up.

It is not necessary to divide the digital bus between physical plugs inthe same way as for the analog signal line because in this casecompressed digital data is periodically outputted at time dividedchannels. However, the effect of deciding a path from one item ofequipment to a different item of equipment is the same as if theconnection were carried out using an analog signal line. Also, when oneitem of equipment is handling a number of channels at the same time, itis necessary to be able to discriminate between these channels. Virtualplugs are therefore set up in this embodiment, so that channels can bediscriminated between during inputting and outputting. Input and outputis also set up separately for these virtual plugs in the same way as foranalog plugs.

FIG. 12 is a view of an example of a virtual plug occurring in thecommunications system for this invention. In the following description,the virtual plug will be referred to as the digital plug. Here, thedigital plug is a register decided by the address, with 4 bytesexpressing 1 plug. Input plug 1 is represented by the 4 bytes foraddresses 00H to 03H, and input plugs 2, 3 and 4, are-represented byaddresses 04H to 07H, 0AH to 0BH and 0CH to 0FH, giving a maximum of 4.Also, output plug 1 is represented by the 4 bytes from addresses 10H to13H, output plugs 2, 3, and 4 are represented by addresses 14H to 17H,18H to 1BH and 1CH to 1FH, giving a maximum of 4. The input/output plugsshould only be set at to the number of plugs which the equipment can useat any one time. For example, with equipment which can only handle 2input/output systems at a time, the regions in the diagrams [ . . . ]become empty registers. As the addresses for the input/output plugsoccurring at each item of equipment are then the same, each item ofequipment is aware of the plug addresses for each of the other items ofequipment. Each item of equipment can therefore read and write to itsown plugs or to plugs for other items of equipment easily.

If the plug enable for the input plug is set to one, the digital I/Freceives synchronous communications packets for information signals fromthe channel set by the channel number (However, just completingconnections with the outside does not by itself change the conditionswithin equipment such as the condition of the input selector etc., sothat inputting is not actually carried out simply as a result of theconditions within the equipment). Clearing the plug enable for the inputplug to 0 will stop the digital I/F from receiving signals. Other fieldsfor the plug are also cleared to 0 at this time. When the signalconnector with the transmitting equipment is being protected, the LSBfor the PC (Protect Counter) for the input plug is set to 1 and whenthere is no protection this is cleared to 0.

If the plug enable for the output plug is set to 1, the digital I/Ftransmits synchronous communication packets for the information signalto the channel set according to the channel number, at a transfer speeddesignated by the data rate (DR) while using the band expressed byBandwidth (internal equipment conditions such as the playback output forthe VTR etc. do not change simply as a result of the completion of anexternal connection. Actual outputting is therefore not carried outsimply depending upon the conditions within the equipment). If the plugenable for the output plug is cleared to 0, the digital I/F stopstransmitting signals. Other fields for the plug are also cleared to 0 atthis time. The PC for the output plug is incremented by 1 when thesignal connections with the receiving equipment are protected and isdecremented by 1 where there is no protection. In this way, equipmentmaking protection requests can be counted.

These plugs can therefore rewrite themselves or can be rewritten fromother items of equipment. It is, however, necessary when the PC becomes“0” that rewriting should take place in order to ensure protection. Thesymbols [—] occurring at each plug are reserved bits.

An environment which is completely the same as that for the analog plugscan therefore be provided by keeping the digital plugs separate atinput/output in this way. Also, connections between digital plugs andinternal equipment connections are kept independent.

6. A specific example of connection control using a digital plug.

The following is a description, with reference to FIG. 13, of connectioncontrol when the output for the MDP in FIG. 1 is recorded by the VTR 2.Here, FIG. 13( a) shows the communication sequence and FIG. 13( b) showsthe commands.

First, the MDP receives a command so that the deck output from thecommand master (editor) is outputted to the digital plug (communication1). If the MDP outputs the deck output to a digital plug, the resultingplug number (here this is plug 1) is transferred to the command master(communication 2).

The VTR 2 then receives a command so that a connection is made from thecommand master to the digital plug and on to the deck (communication 3).If the VTR 2 connects the digital plug to the deck, the resulting plugnumber (in this case this is digital plug 1) is transferred to thecommand master (communication 4).

The connection described above between the sub-device within theequipment and the digital plug uses the DDB command withoutmodification. In this way, if the digital plug it is intended use isknown, communications can be carried out so that the command master canactually be connected to its fellow digital plug. In order to set up thedigital plugs for the source equipment and destination equipment, atransaction is to be transmitted (communication 5) so that a channelnumber, transmission speed and band width can be written at the digitaloutput plug 1 for the MDP. A further transaction is then transmitted(communication 6), to prepare for the writing of the channel number atthe digital input plug 1 for the following VTR 2.

Here, the communications 5 and 6 are not DDB commands. The transactionknown as read-write-rock, for designating the opposing register addressand writing the data is provided at P1394. With regards to DDB commandssuch as, “exchange command”, data is written so as to be exchangedbetween command registers, which is achieved by then interpreting thedata. With regards to this, communications 5 and 6 can utilize thetransactions more directly. The instruction, “set up the opposingdigital plug” can then be executed by designating the opposing addressas well as the digital plug address and then writing in. Also, “find outthe input/output conditions for the opposing digital plug” can beexecuted by designating the digital plug address and then carrying atthe reading operation.

In this embodiment, connections between sub-devices within the equipmentand the digital plugs (communications 1 to 4) use higher order commandspresent in the DDB commands, and plug connections between items ofequipment (communications 5 and 6) use digital bus protocol. That is tosay, the control system for making connections between digital plugs andthe control system for making connections between sub-devices within theitems of equipment and digital plugs are independent. It follows thatmatching can be achieved by digital plugs without having to insert aconception of the digital bus characteristics to a connection controlsystem within existing equipment, so that interchangeability withexisting command sets can be maintained.

7. An example of equipment equipped with digital plugs.

FIG. 14 is a view showing an example structure for a VTR equipped withdigital plugs. Here, the digital plugs P1 and P2 for input and outputare set up in the ram area within a communications controllingmicrocomputer. The communications controlling micro computer (which isequivalent to an AVC sub-device) takes data from the digital I/F andsends a control signal for controlling the digital I/F or the switchboxsub-device so as to activate the designated task. For example, when atransaction of the kind in communication 6 in FIG. 13 going to thedigital plug P1 is received, a control signal is sent so as to controlthe digital I/F so that an information signal from the channel numberthat is written in is inputted. If the kind of command in communication3 in FIG. 13 is received, a control signal is sent to control theswitchbox sub-device so that the deck sub-device is connected at thedigital plug P1.

FIG. 15 is a view showing a further example of a structure for a VTRequipped with digital plugs. Here, transactions going to the digitalplugs access registers within the digital I/F directly so that thedigital plugs P1 and P2 for input and output may actually exist in theregister area within the digital I/F. The digital I/F then activates thedesignated path. The micro computer for communication control may thentransmit the conditions at which the digital plugs are set up andactually operating as data, if necessary.

FIG. 16 is a view showing an example structure for a hard disc equippedwith digital plugs. Here, the digital plug P1 for input and output isset up within the digital I/F. As the functional unit within theapparatus (sub-device) is a single disc unit, there is a single digitalplug for input/output and a connection is always made with thesub-device. Connection control such as DDB etc. is therefore notnecessary, and compatibility with a digital bus can be achieved even ifthere is no microcomputer for communications control. It is thereforepossible to manufacture low cost equipment.

Also, one input/output plug may now be set up for one digital buschannel number. In this way, it is only necessary to set up digitalplugs for the numbers of channels present in the system and it is nolonger necessary to write the channel number at the digital plug.

1. A communication method for a communication system in which aplurality of electronic apparatuses are connected via a digital busconfigured for transferring isochronous communication packets labeledwith channel numbers and asynchronous communication packets in a certaincommunication cycle, wherein information signals are transmitted on saidisochronous communication packets and control signals are transmitted onsaid asynchronous communication packets, and wherein each of saidelectronic apparatuses have digital output plugs which output saidisochronous communication packets or digital input plugs which inputsaid isochronous communications packets, said method comprising thesteps of: controlling said digital output plugs implemented as registersto which respective addresses are allocated at a transmitting apparatus,wherein the register for said digital output plug includes a channelnumber field indicating a channel number; controlling said digital inputplugs implemented as registers to which respective addresses areallocated at a receiving apparatus, wherein the register for saiddigital input plug includes a channel number field indicating a channelnumber; using a first counter included in the digital output plugcontrol register at a transmitting apparatus to protect connections withreceiving apparatuses; using a second counter included in the digitalinput plug control register at a receiving apparatus to protectconnections with transmitting apparatuses; transmitting said informationsignals from one digital output plug at the transmitting apparatus ontoone channel; and receiving said information signals on said one channelat each of digital input plugs in a plurality of receiving apparatuses.2. The communication method according to claim 1, wherein said registersinclude information indicating whether or not said information signalscan be transmitted or received.
 3. The communication method according toclaim 1, wherein said registers include information relating to a datarate.
 4. The communication method according to claim 1, wherein saidregisters include information relating to a band.
 5. The communicationmethod according to claim 1, wherein said digital bus is an IEEE 1394bus.